Three male sheep of about 25 kg body weight fitted with a cannula into the rumen and reentrant
cannula in the proximal duodenum and in the distal ileum were used for this study. Sheep No. 1 was
infused intraruminally with 15N urea ( 1 g/d, 95 atom% 15N) for labelling with 15N, Nos. 2 and 3 with
unlabelled urea. A ll animals were fed 800 g DM /d of a hay and concentrate diet (40 : 60) containing
15.4 % crude protein and 15.3 % crude fibre, divided into 6 feeding portions per day. After reaching
a quasi-steady state in the 15N level of animal No. 1, passage of total N and 15N throughout the
duodenum and the ileum, N excretion in faeces and urine were estimated. On day 7 and 8 of the
experiment the duodenal and ileal digesta were exchanged between the labelled animal (No. 1) and the
unlabelled ones (No. 2, 3) according to the respective scheme. Digesta flow was measured directly
during 48 h and 3% aliquots were sampled for analysis of N and 15N content. The contents of N and 15N were also estimated in faeces, urine and blood. The obtained data were used for calculation of the
passage and absorption of exogenous N and the secretion, absorption and reabsorption of endogenous
N in three digestive sections from mouth to proximal duodenum, from duodenum to ileum, and from
ileum to rectum.
The flow of total N , exogenous N and endogenous N decreased from duodenum to ileum and
faeces, but the relative content of endogenous N increased from 36 to 54 %. N-secretion was highest
in the first section of the digestive tract (9.9 g N/d = 60% of the secretion in total digestive tract) and
absorption was highest in the second section (14.1 g N/d = 46 % of total absorption). Endogenous
origin N was about 54 % of faecal N. Faecal loss, 2.0 g endogenous N/d, was only about 12% of the
total endogenous N (16.5 g N) secreted into the lumen during the intestinal passage of digesta. Total
reabsorption of endogenous N amounted to 88%. The results demonstrate the high dynamics of N
metabolism during digestion in ruminants.

CITATIONS(1):

1.

Monitoring digestibility of forages for herbivores: a new application for an old approach L.L. VanSomeren, P.S. Barboza, D.P. Thompson, D.D. GustineCanadian Journal of Zoology

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